1. Field of the Invention
This invention relates to a shift register in an electronic circuit being operated by a pulse-cut clock signal, and to a drive circuit, an electrode substrate and a display device that include the shift register.
2. Description of the Related Art
Display devices as represented by liquid crystal display devices are used in various instruments because of their thin profile, light weight and low power consumption. In recent years, an active matrix liquid crystal display device, in which transistors are disposed for each pixel, has become widespread in notebook computers or personal digital assistants. Technology for forming polysilicon thin-film transistors (p-SiTFT's) at a relatively low-temperature process has been established. The p-SiTFT's possess higher electron mobility in comparison with amorphous silicon thin-film transistors used in conventional liquid crystal display devices. Accordingly, downsizing of the transistors has been effectuated. This technology has realized the integral formation of a pixel unit and a drive circuit on an electrode substrate in the same fabricating process. The pixel unit includes transistors disposed in plural on intersections of a plurality of scan lines and a plurality of signal lines. The drive circuit drives each transistor.
There are two kinds of drive circuit. One is a scan line drive circuit for outputting pulses to the scan lines. The other is a signal line drive circuit for outputting pulses to the signal lines. Each of the drive circuits includes a plurality of electrically cascaded shift registers. Each shift register shifts a phase of an inputted signal and then outputs the signal. The scan line drive circuit outputs horizontal scan pulses to the respective scan lines while shifting a phase of each pulse by one stage. The signal line drive circuit outputs vertical scan pulses to analog switches provided in plural on the signal lines while shifting a phase of each pulse by one stage. Image signals are inputted to the analog switches from outside, and the signal line drive circuit outputs the image signals to the respective signal lines.
In order to facilitate manufacturing, there is a case in which these shift registers are merely composed of either p-channel metal-oxide semiconductor (p-MOS) transistors or n-channel metal-oxide semiconductor (n-MOS) transistors. Literature disclosing such shift registers includes: U.S. Pat. No. 5,222,082; Japanese Unexamined Patent Publication No. 2000-155550; SID 00 DIGEST, pp 1116-1119; and EURO DISPLAY 99 LATE-NEWS PAPER, pp 105-109.
Incidentally, regarding the horizontal scan pulses or the vertical scan pulses, if temporally adjacent pulses overlap each other, such overlap may incur display unevenness because an image signal may be written into a pixel which is not supposed to receive the signal, or because the image signal is not adequately written into a pixel which is supposed to receive the signal. A method for preventing the unevenness is so-called “pulse cut”. This method provides time intervals between the leading-edge and the trailing-edge of a plurality of clock signals inputted to the shift registers.
However, if a pulse-cut clock signal is inputted to a shift register, time deviation occurs among transistors in the shift register. As a result, the transistors constituting an output circuit of the shift register may not be turned on and off properly, whereby voltage levels of outputted signals may become unstable.